1. Field of the Invention
This invention relates to the use of 3-(4-alkylbenzoyl)-acrylic acid as corrosion inhibitor in lubricating oils and lubricating greases based on mineral oils.
Industrial processes in which metal surfaces, particularly surfaces of iron and iron alloys, come into contact with oils or oil-containing aqueous emulsions under extreme temperature and pressure conditions are hampered by resultant corrosion of the metal surfaces. Processes of the type in question include, for example, industrial cooling processes, processes for cleaning metal surfaces, and processes for machining metal surfaces, such as drilling, cutting and rolling. Although oils or oil-containing emulsions are typically used in these processes, the effect of exposure to even the relatively small amounts of water usually present in these compositions presents corrosion problems. The built-up corrosion of the metal machine parts coming into contact with these oils or oil-containing liquids leads to a drastic reduction in the useful life of the machinery, and substantially precludes subsequent prophylactic treatment of the metal surface, such as application of a corrosion-inhibiting surface layer by phosphating or lacquering.
2. Statement of Related Art
Accordingly, it has long been known to add corrosion inhibitors to such oil-based liquids. Numerous compounds and mixtures of various compounds are known for use as corrosion inhibitors in predominantly oil-containing liquids or pure oils. For example, German published patent application No. 11 49 843 describes semiamides of saturated or unsaturated dicarboxylic acids and salts thereof with aliphatic primary amines as corrosion-inhibiting additives for fuel oils and lubricating oils. Although additives such as these distinctly improve the corrosion resistance of lubricating oils, they show a very marked tendency towards foaming which is unacceptable in additives of this type. Alkali or amine salts of sulfonamidocarboxylic acids for use as corrosion inhibitors which have a good lubricating effect with very little tendency towards foaming are described in German published patent application No. 12 98 672. However, corrosion-inhibiting preparations containing these compounds are disadvantageous insofar as elaborate processes are required for their production, and, because of their relatively high content of sulfonamide groups, they are least potentially toxic and occasionally exhibit toxic effects.
In addition, synthetic sulfonates developed from petroleum sufonates are known to inhibit corrosion in oil or oil-containing systems, cf. Ullmann's Encyclopadie der techn. Chem., Vol. 18, 4th Edition (1979), pp. 1/2; Winnacker, Kuchler, Chem, Technologie, Vol. 4, Org. Technologie II, 3rd Edition (1972) p. 475. This class of compounds also has disadvantages, however, inasmuch as they are not biodegradable and, hence, cannot be used in processes which might impact on the environment through waste water or ground water contamination with resulting ecological damage.